Planets are intentionally given no surface-to-space weaponry.
The other side of this is that bombardment is very supply and time intensive.
Ground combat is where its at. The best way to damage a planet's hitpoints is to let your tanks bLast away, since they come in large numbers and don't need to resupply. Plus as a bonus you get to capture the planet when you win
PS:
About the huge components, yes I'm aware that it is insanely large.
I'm going to cut it back to perhaps 5x5x5, so its 1/8th the size. Should help keep the game out of the swap file on most PCs.